well, so long as i'm within 3U i'm fine. i need at least 1U, ideally 3U for non-computer equipment in the rack. i'd be going for an ultra-dense fileserver here. i know i can get .5tb (RAID-5) in 1U easily enough. i should be able to get 1.5tb (RAID-5) in 2U without too much effort (dual power supplies, 3-ware RAID controller on a riser, all 250gb drives...).